Rōkyoku is a traditional Japanese narrative singing style featured within the documentary context of the film. This musical form involves rhythmic intonation by a singer, the rōkyokushi, accompanied by a shamisen player, the kyokushi. They perform dramatic stories drawing from historical events, folklore, and themes such as loyalty and emotional conflict. Performances blend sung sections, known as fushi, with spoken narrative, called tanka, creating a melodramatic atmosphere.

In the film, rōkyoku contributes to the soundtrack and thematic presentation. Musician Takeharu Kunimoto is noted for his shamisen performances, carrying his instrument in a distinctive Harley Davidson case. This highlights a blend of traditional artistry with contemporary elements. The musical style is interwoven with the film's exploration of Miyamoto Musashi's legacy, using its historical and cultural resonance to complement the documentary's examination of samurai history and myth.